The invention relates to a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, the device comprising
input means for receiving the binary source signal, PA0 merging means for merging a q-bit merging word at equidistant positions in the binary source signal in response to a control signal, so as to obtain a composite binary source signal, PA0 converting means for converting the composite binary source signal into said binary channel signal, PA0 control signal generator means for generating said control signal, PA0 output means for supplying said binary channel signal. The invention also relates to a device for decoding a stream of data bits of a binary channel signal obtained by means of the encoding device, so as to obtain a stream of databits of a binary source signal, to a recording device comprising the encoding device, to a record carrier obtained with the recording device and to a method of encoding the source signal.
An encoding device mentioned in the foregoing is known U.S. Pat. No. 5,477,222 (PHN 14448). The document discloses a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, satsifying a (1,8) runlength constraint. That means that, in a serial datastream of the channel signal at mimimum one `zero` and at maximum eight `zeroes` are present between two consecutive `ones` in the channel signal. It should be noted in this respect that normally an additional precoding step, such as a 1T precoding, is applied to the (1,8) constrained sequence, resulting in a runlength limited sequence with minimum runlength 2 and maximum runlength 9.
The known conversion is parity preserving. `Parity preserving` means that the parity of the n-bit source words to be converted equal the parity (after modulo-2 addition) of the corresponding m-bit channel words in which they are converted. As a result, the n-to-m conversion device as claimed does not influence the polarity of the signal.
As the conversion is parity preserving, an efficient DC control can be applied, such as by inserting DC control bits in the datastream of the source words.